They all have connotations opposite of gentle but it depends if talking about a person’s weight it would most likely be large but in general I think it would be big
B would be considered the most positive of the options given.
Do you have an example of the "text"? It's difficult to answer a question like this without seeing the text itself.
Main pieces of imagery can be something describing how stuff looks, smells, feels, or what it sounds like. It should create a picture in your head. So whatever helps illustrate the text for you is an example of imagery! Hope this helps!
